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  • 1.
    Brolin, Karin
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Halldin, Peter
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Development of a finite element model of the upper cervical spine and a parameter study of ligament characteristics2004In: Spine, ISSN 0362-2436, E-ISSN 1528-1159, Vol. 29, no 4, p. 376-385Article in journal (Refereed)
    Abstract [en]

    Study Design. Numeric techniques were used to study the upper cervical spine. Objectives. To develop and validate an anatomic detailed finite element model of the ligamentous upper cervical spine and to analyze the effect of material properties of the ligaments on spinal kinematics. Summary of Background Data. Cervical spinal injuries may be prevented with an increased knowledge of spinal behavior and injury mechanisms. The finite element method is tempting to use because stresses and strains in the different tissues can be studied during the course of loading. The authors know of no published results so far of validated finite element models that implement the complex geometry of the upper cervical spine. Methods. The finite element model was developed with anatomic detail from computed tomographic images of the occiput to the C3. The ligaments were modeled with nonlinear spring elements. The model was validated for axial rotation, flexion, extension, lateral bending, and tension for 1.5 Nm, 10 Nm, and 1500 N. A material property sensitivity study was conducted for the ligaments. Results. The model correlated with experimental data for all load cases. Moments of 1.5 Nm produced joint rotations of 3degrees to 23degrees depending on loading direction. The parameter study confirmed that the mechanical properties of the upper cervical ligaments play an important role in spinal kinematics. The capsular ligaments had the largest impact on spinal kinematics (40% change). Conclusions. The anatomic detailed finite element model of the upper cervical spine realistically simulates the complex kinematics of the craniocervical region. An injury that changes the material characteristics of any spinal ligament will influence the structural behavior of the upper cervical spine.

  • 2.
    Brolin, Karin
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Halldin, Peter
    KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701).
    Leijonhufvud, I.
    The effect of muscle activation on neck response2005In: Traffic Injury Prevention, ISSN 1538-9588, E-ISSN 1538-957X, Vol. 6, no 1, p. 67-76Article in journal (Refereed)
    Abstract [en]

    Prevention of neck injuries due to complex loading, such as occurs in traffic accidents, requires knowledge of neck injury mechanisms and tolerances. The influence of muscle activation on outcome of the injuries is not clearly understood. Numerical simulations of neck injury accidents can contribute to increase the understanding of injury tolerances. The finite element (FE) method is suitable because it gives data on stress and strain of individual tissues that can be used to predict injuries based on tissue level criteria. The aim of this study was to improve and validate an anatomically detailed FE model of the human cervical spine by implement neck musculature with passive and active material properties. Further, the effect of activation time and force on the stresses and strains in the cervical tissues were studied for dynamic loading due to frontal and lateral impacts. The FE model used includes the seven cervical vertebrae, the spinal ligaments, the facet joints with cartilage, the intervertebral disc, the skull base connected to a rigid head, and a spring element representation of the neck musculature. The passive muscle properties were defined with bilinear force-deformation curves and the active properties were defined using a material model based on the Hill equation. The FE model's responses were compared to volunteer experiments for frontal and lateral impacts of 15 and 7 g. Then, the active muscle properties where varied to study their effect on the motion of the skull, the stress level of the cortical and trabecular bone, and the strain of the ligaments. The FE model had a good correlation to the experimental motion corridors when the muscles activation was implemented. For the frontal impact a suitable peak muscle force was 40 N/cm2 whereas 20 N/cm2 was appropriate for the side impact. The stress levels in the cortical and trabecular bone were influenced by the point forces introduced by the muscle spring elements; therefore a more detailed model of muscle insertion would be preferable. The deformation of each spinal ligament was normalized with an appropriate failure deformation to predict soft tissue injury. For the frontal impact, the muscle activation turned out to mainly protect the upper cervical spine ligaments, while the musculature shielded all the ligaments disregarding spinal level for lateral impacts. It is concluded that the neck musculature does not have the same protective properties during different impacts loadings.

  • 3.
    Brolin, Karin
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Hedenstierna, Sofia
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Halldin, Peter
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Bass, Cameron
    Center for Applied Biomechanics, University of Virginia, Charlottesville.
    Alem, Nabih
    US Army Aeromedical Research Laboratory, Fort Rucker.
    The importance of muscle tension on the outcome of impacts with a major vertical component2008In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 13, no 5, p. 487-498Article in journal (Refereed)
    Abstract [en]

    The hypothesis that muscle tension protects the spine from injuries in helicopter scenarios was tested using a finite-element model of the human head and neck. It was compared with cadaver crash sled experiment with good correlation. Then, simulations were performed with a sinusoidal velocity (5-22 G) applied at T1 60° to the horizontal plane. The model with relaxed muscle activation had delayed and decreased peak head rotation compared with passive properties only. Full muscle activation decreased the injury risk for the 13.5-22 G impacts. A sensitivity study of the impact angle showed a very slight variation of the resulting neck flexion, and 1° change affected all ligament injury predictions less than 4%. Finally, simulations with helmets resulted in increased ligament and disc strains with increasing helmet mass and with an anterior or inferior shift of the centre of gravity. It is concluded that the hypothesis seems to hold.

  • 4.
    Brolin, Karin
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Nordberg, Axel
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Stability and fibre reinforced adhesive fixation of vertebral fractures in the upper cervical spine2006In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, p. 151-152Article in journal (Refereed)
  • 5.
    Halldin, Peter
    et al.
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Brolin, Karin
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Hedenstierna, Sofia
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Aare, Magnus
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    von Holst, Hans
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    Finite element analysis of the effects of head-supported mass on neck responses: Complete phase one report, United states army european research office of the U.S army2004Report (Refereed)
  • 6.
    Halldin, Peter
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Brolin, Karin
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Hedenstierna, Sofia
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Aare, Magnus
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Finite element analysis of the effects of head-supported mass on neck responses: Complete phase two report, United states army european research office of the U.S. army2005Report (Refereed)
  • 7.
    Halldin, Peter
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Hedenstierna, Sofia
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Brolin, Karin
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Finite element analysis of the effects of head-supported mass on neck responses: Complete phase three report, united states army european research office of the U.S.army2006Report (Refereed)
    Abstract [en]

    The objectives for the whole project were to: I. determine the relationships between head supported mass and the risk of neck injuries. The results should be used in a Graphical user interface. In this phase three report has also the Graphical User Interface (GUI) been evaluated and the question about the how the muscle activation affect the injury risk. II. to develop and implement a 3D numerical muscle model. Results: I. The KTH neck model has successfully been used to generate results for the GUI. Results from all simulations have been reported and sent to Titan Corporation that is contracted by USAARL to program the GUI. The GUI that uses an interpolation method to calculate the neck injury risk for a general helmet with a user defined HSM configuration shows to give realistic interpolated values compared to the FE model of the neck. II. The 3D muscle model for the cervical spine includes 22 pairs of muscles. The solid muscle model showed to stabilize the vertebral column better than the spring muscle model. The model is still under evaluation and need further validation to be used in the HSM evaluation project.

  • 8.
    Hedenstierna, Sofia
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Halldin, Peter
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Brolin, Karin
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Evaluation of a combination of continuum and truss finite elements in a model of passive and active muscle tissue2008In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 11, no 6, p. 627-639Article in journal (Refereed)
    Abstract [en]

    The numerical method of finite elements (FE) is a powerful tool for analysing stresses and strains in the human body. One area of increasing interest is the skeletal musculature. This study evaluated modelling of skeletal muscle tissue using a combination of passive non-linear, viscoelastic solid elements and active Hill-type truss elements, the super-positioned muscle finite element (SMFE). The performance of the combined materials and elements was evaluated for eccentric motions by simulating a tensile experiment from a published study on a stimulated rabbit muscle including three different strain rates. It was also evaluated for isometric and concentric contractions. The resulting stress-strain curves had the same overall pattern as the experiments, with the main limitation being sensitivity to the active force-length relation. It was concluded that the SMFE could model active and passive muscle tissue at constant rate elongations for strains below failure, as well as isometric and concentric contractions.

  • 9.
    Hedenstierna, Sofia
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Halldin, Peter
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Brolin, Karin
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Development and evaluation of a continuum neck muscle model2006In: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 39, no Supplement 1, p. 150-Article in journal (Refereed)
  • 10.
    Nordberg, Axel
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Brolin, Karin
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering.
    Beckman, Anders
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Vertebral fractures fixation with composite patch fibre reinforced adhesives2007In: Bio-medical materials and engineering, ISSN 0959-2989, E-ISSN 1878-3619, Vol. 17, no 5, p. 299-308Article in journal (Refereed)
    Abstract [en]

    Purpose: The aim is to investigate fixation of cervical vertebral fractures by patching it with a composite laminate of adhesive and fibres, in comparison with use of only adhesives. Material and methods: The composite fixation was tested on bonded roe deer vertebrae. 25 specimens were sawed in two halves, creating a generic fracture, and thereafter bonded. The adhesives used were a dental system, Scotchbond XT, and a cyanoacrylate, M-bond 200. The fibres used were unidirectional carbon fibres and randomly distributed E-glass fibres. The composites were applied as a 7 mm wide patch circumferential along the induced fracture. Reference specimens for comparison were also made. The ultimate tensile strength was tested in an Instron 5567. The failure site was examined with a microscope. Strain vectors were tracked using Digital Speckle Analysis. Results: Scotchbond XT + E-glass fibres gave best results, with a tensile strength of 3.5 N/mm circumferential length (24.3% of reference). All composites had lower stiffness than cortical bone. The dental adhesive fibre composites gave better results than the cyanoacrylate fibre composites. In all cases fibre reinforced adhesive composite gave better results than adhesive without fibre reinforcement. Conclusion: Fibre-adhesive composite is a promising technique for fixating cervical vertebral fractures.

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